A condition where a program continues to request more memory from an operating system, and doesn't tell the operating system when it is no longer using the memory. Programs with memory leaks (which can be considered a BUG) can end up using all of the memory available, or at least enough to cause performance problems.
A loss of usable storage space caused by the application's failure to correctly reclaim the memory occupied by the current KB's transient items.
Applications that require temporary memory request the memory from the operating sytem. When the application is done using the memory, it is supposed to tell the operating system so the operating system can use the memory for other applications. An application that fails to return the memory it had been given creates a " memory leak" - a situation in which some memory that is no longer in use is not available for future use.